The invention concerns a hydropneumatic pressure intensifier of the type categorizing the main claim. Hydropneumatic pressure intensifiers of this type are used mainly for machine tools and function with alternating pressures, i.e. high pressure and low pressure in the working chamber, and having pneumatic and hydraulic working means exhibiting alternating rapid pressure increases and changes between overpressure and underpressure. This affects in particular the sealing rings of the seals between the working piston and the cylindrical wall of the working chamber and/or the sealing ring in the connecting bore between the working chamber and the storage chamber, wherein, at low pressure, the plunger piston is repeatedly introduced into and removed out of the sealing ring. This plunging process requires appropriate design of the sealing ring to ensure that when the plunger piston is immersed, the end face of the plunger piston does not clamp on the sealing ring side facing same, wherein the radial forces produced by the rubber-elastic tensioning ring, which have a corresponding effect on the clearance of the sealing ring, have to be taken into consideration. The sealing ring must have an appropriately large radial stiffness and guarantee static and dynamic sealing. The sealing ring must, of course, have high wear resistance and extrusion resistance with long service life and should facilitate assembly without deformation of the sealing edges. The sealing ring must, in particular, resist extremely high loads, i.e. high pressures and pressure shocks.
A known hydropneumatic pressure intensifier of the type categorizing the invention (EP 0 579 073 B1 and DE-PS 32 25 906 C2) provides the optimum preconditions for the expert, in particular for the producer of the patented sealing ring. It is thereby assumed that the high pressure can directly act on the sealing ring from one side. Due to the step provided in the direction of the working chamber on the circumferential surface of the sealing ring facing the piston, this sealing ring is axially loaded and pressed against the end wall, facing away from the working chamber, of the annular groove receiving the sealing ring without producing actual deformation of the sealing ring to thereby provide the intended sealing support of the sealing surface on the piston surface. Other sealing rings produced by this sealing ring manufacturer which are made from softer distortable material would not be used by one of average skill in the art, since their radial stiffness is either too low for immersion or they cannot withstand the high pressures and dynamic wear.
Practice has moreover shown that the above-mentioned sealing ring used for hydropneumatic pressure intensifiers consists of a material which is distributed under the trademark Turcon T46 which has metallic inclusions producing increased friction between the sealing ring and piston which act like sanding dust at this location. These metallic inclusions may also be caused by friction on the piston due to the hardness of the sealing material. This has, in end effect, the same result as sanding dust and guarantees good sealing and durability or service life due to the structure of the sealing ring while reducing wear on the piston in the sealing area.
In contrast thereto, the inventive hydropneumatic pressure intensifier having the characterizing features of the main claim (in contrast to the expectations of one of average skill in the art and despite the expected relatively easy incorporation of the sealing ring due to the associated pressure and friction acting on the piston) not only advantageously provides good sealing and durability, i.e. service life, but also prevents wear in the frictional area between the sealing ring and piston surface. Moreover, in contrast to the expectations of one of average skill in the art, immersion of the plunger piston into the sealing ring is very easy although, due to the increased softness, the sealing ring can be deformed by the tensioning ring in the direction of the sealing surface. Such a relatively soft sealing ring with corresponding cross-sectional design is known per se (EP 0 670 444) as is the typical deformation of this sealing ring (EP 0 582 593). The material used is distributed by the producer under the trademark Zurcon: the sealing ring itself under the trademark Rimseal. The producer recommends use of this seal only as a secondary seal especially for relatively high pressures. It was developed explicitly as such and only in this way can safe sealing of thin oil films be guaranteed, in particular, with low secondary pressures. The material is polyurethane with Shore D 58. One of average skill in the art uses such a sealing ring in particular if the piston exhibits a slight tilting movement with respect to its cylinder. Immersion of a plunger piston into such a soft material is not considered to be acceptable by one of average skill in the art. The above-mentioned relatively hard sealing ring is recommended for the primary seal and is used in conventional hydropneumatic intensifiers. Due to the relatively soft material, which is also absolutely free from metallic inclusions, the piston surface is not subjected to frictional wear which could lead to the above-mentioned sanding dust effect.
In accordance with an advantageous embodiment of the invention, the opposite walls of the annular groove or the like extend essentially parallel to one another. As a result thereof, the sealing ring is loaded with unilateral forces produced by the conical travel of the end wall and acting in the direction of the piston.
In accordance with a further advantageous embodiment of the invention, the plastic material of the sealing ring does not have any metallic inclusions. This has the principal advantage of preventing mechanical wear of the piston surface.
In accordance with another advantageous embodiment of the invention, the sealing ring consists of a plastic material produced by the company Busak and Shamban under the name Zurcon with the trademark Rimseal and made from a special polyurethane 58 Shore B.
In accordance with another advantageous embodiment of the invention, the working piston comprises a pneumatically loaded collar for its fast stroke drive, wherein the rear side of the seal is alternately loaded with pneumatic working pressure and with the lowermost pressure.
In accordance with another advantageous embodiment of the invention, the sealing ring is directly loaded at the working chamber side with the pressure of the working chamber, without any other intermediate sealing elements.